Automatic telephone system



July 15 1-924. 1,501,287

c. E LOMAX AUTOMATIC TELEPHONE SYSTEM Original Filed Aprii 19. 1920 :5 Sheets-Sheet 1 AAAAA l Alllll ""I' III." AlAAAAli -IAlllll j'nuanlur" LCIZEEEQOE.LUHIE 7 5 July 15 1924. 1,501,287'

c. E. LOMAX AUTOMATIC TELEPHONE SYSTEM Original Filed April 19. 1920 5 Sheets-Sheet L'Zarsnca E. Lnmax HIT y:

Jul 15 ,1924. 1,501,287:

C. E. LOMAX AUTOMATIC TELEPHONE SYSTEM 0 i eets-Sheetfi ----Imfiltifv j Elarancs E Lnmax Patented July 15, 1924.

UNITED STATES 1,501,287 PATENT OFFICE.

CLARENCE E. LOMAX, O13 CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed April 19, 1920, Serial No. 374,886. Renewed April 11, 1924.

T all whom it may concern:

Be it known that I, CLARENCE E. LOMAX, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

My invention relates in general to automatic telephone systems, but more especially to private automatic systems or exchanges for use in factories, mercantile establishments, etc.; and the object of the invention may be stated to be the'provision of a private automatic exchange, and suitable interconnecting trunk circuits therefor, which is adapted for use as part of a large manual system.

Private automatic systems of the above general character have come into wide use,

not only in cities having full automatic telephone systems, but recently also in cities having manual systems. A demand has arisen therefore for a more suitable trunk circuit for interconnecting a manual main exchange with an automatic private branch exchange and it is to meet this need that I have devised the improved trunk circuit. which with the associated equipment at the main and branch exchange ends thereof forms the subject matter of this application. In the drawings, comprising Figs. 1, 2, and 3, I have shown by means of the usual circuit diagrams a trunk circuit embodying my invention which extends from the jack J in a manual exchange, Fig. 1, to a private automatic exchange, certain essential parts of which are shown in Figs. 2 and 3. At the latter point the trunk line extends through an attendant operators position (Fig. 2) where certain relay equipment, lamp signals, etc., are provided, and terminates in an automatic connector switch which is indicated by the reference character H, Fig. 3.. The connector H when used as shown herein is usually called an incoming connector and is one of a plurality of simi lar connectors in which the main to branch exchange trunk lines terminate. These connectors are ordinary vertical and rotary switches of the Strowger type and have access to the local lines in the branch exchange, pile of which is the line extending to station In order to handle outgoing calls from the local lines each line is provided with an -individual line or trunk selecting switch, the line switch associated with the line of station A being indicated in Fig. 3 by reference character C. All of these line'switches may have common access to a group of local connectors (not shown) which have access to the local lines the same as do the incoming connectors like the connector H. The local connectors are preferably of the type in which provision is made for an automatic rotary movement on two of the levels, in order that access may be had to the trunk lines connecting with the main exchange, and also to a group of trunk lines extending to the attendant operators position. The multiple bank contacts 150, 151, and 152 in the upper left hand corner of Fig. 3 are located in the bank of a local connector and are multipled to similar contacts in other similar connectors. The local switching mechanism forms no part of the invention, but since on this account no local connector is shown, reference is made to the U. S. patent to Martin, No. 1,291,990, which shows how a connector may be given an automatic rotary or trunk selecting movement on a certain level.

Having indicated the scope of my invention in general terms, I will now proceed to explain the operation of the particular embodiment thereof which I have shown in the drawings. For this purpose it will be as sumed that the subscriber at station A, Fig. 1, desires to obtain connection with the subscriber at station A, Fig. 3. hen the receiver is removed at station A, a circuit is completed for the line relay 2, and this relay is energized to light the line lamp L in the usual manner. Upon perceiving the signal, the operator will respond by inserting the answering plug of an idle cord circuit, cord circuit 0 for example, in the jack J. By this operation a circuit is com pleted over the sleeve of the jack which 111- cludes the cut-off relay 3 and the supervisory lamp L in series. The cut-oifrelay is energized and cuts off the line relay 2, thereby extinguishing the line lamp L; but since the receiver is oil the hook at the calling station the supervisory relay 4: in the cord circuit will energize at once and the lamp L will be shunted out and will not be lighted. 1

The operator will now throw the key K by the operation of relay to listening position and will ascertain the number of the station with which the calling party desires a connection. This being the station A in the branch exchange, whose number maybe assumed to be No. 67, the operator will next test the outgoing trunks extending to the branch exchange with the tip of her calling plug in order to select an idle trunk. Assuming that the trunk line shown is the trunk selected, the operator will insert the calling plug in jack J whereupon a circuit will be established over the sleeve of the jack which includes supervisory lamp L and the cut-off relay 12. Relay 12 at once energizes and at its armature 16 closes the following circuit for the line relay 101 of the connector H; ground at G winding of relay 13, lower right hand winding of repeating coil R, armature 16 and its Wor ring contact, contact springs of key K, conductor 31, contact springs of key K resting contact of armature 39 and the said armature, contact spring 10 of key K and itsresting contact, conductor 99, armature 115 and its resting contact, normally closed contact springs controlled by armature 128 of relay 106, and the winding of the line relay 101 to battery. Upon the closure of the above circuit relay 13 and the line relay of the connector H are energized in series, the former being effectiveat this time toopen at its armature 18 a shunt circuit whichwas closed around the condenser C 12. As a result, no current will flow through the supervisory relay 5 and the supervisory lamp L will be lighted.

At the connector H, the line relay 101,

upon energizing, closes a circuit for the slow acting release relay 102 as follows: ground at G ai 'mature 116 and its working contact, 011 normal spring 163 and its resting contact, and the winding of relay 102 to battery. Upon energizing, relay 102 Propares a circuit for the vertical magnet 109 at its armature 119, disconnects the cut-oil relay 100 at the resting contact of its armature 117, and at the working contact of the same armature connects ground G to the conductor 95, which corresponds to the usual release trunk conductor. By the grounding of conductor 95 a ground potential is placed on test contact 151 and its multiples in the banks of the local connectors thereby making the trunk line busy to outgoing calls from the branch exchange. It will be observed also that conductor 95 extends back to the attendant operators position, Fig. 2, where supplies current to the busy lamp I f, malntaming this lamp lighted as long as the trunk line is in use. There is another circuit extending from the connector H back to the lamp L at the attendants posit1on which extends as follows: grounded conductor 95, armature 11 1 of relay 100 and its resting contact, resting contact of armature 127 and the said armature, oft normal spring 161 and its resting contact, conductor 08, resting contact of armature 37 and the said armature, and the lamp L to battery. Lamp L is one of the supervisory lamps provided to give the attendant operator complete supervision. In its lighted condition lamp L indicates that the connector H has been taken for use but has not been operated.

The operator at the main exchange will now perate the calling device key K which is associated with the trunk line in use, thereby inserting her calling device S in the circuit of the line relay 101 of the connector H. The dial of the calling device being now operated in accordance with the tirst digit 6 of the desired number in the branch exchange, a series of six interruptions is produced in the line relay circuit, and the line relay is accordingly deenergized momentarily a like number of times, at each deenergizatio-n transmitting an impulse of current to the vertical magnet as follows: ground at armature 116 and its resting contact, resting contact of armature 125 and the said armature, winding of slow acting series relay 104e, resting contact of armature 132 and the said armature. contact springs controlled by armature 122, working contact oit armature 119 and the said armature, and the winding of the vertical magnet 109 to battery. Responsive to impulses re eeived over the above circuit the vertical magnet operates to raise the switch shaft step by step until the wipers 1 10-112, i11- clusive, stand opposite the sixth level of bank contacts. At the first upward movement of the shaft the ofl'normal springs 161161 are shifted, and at the resting contact of spring 163 the original energizing circuit f the slow acting relay 102 is broken. The slow acting series relay 104 having energized in series with the vertical magnet, however, a new circuit has been es tablished astollows: ground at G armature 116 and its working contact, oil normal spring 163 and its working contact, armature 121 and its left hand working con tact, and the winding of relay 102 to battery. Relay 102 receives current impulses over the above circuit to maintain it energized during the vertical movement. Relay 101 also remains energized during the vertical movement, being in series with the vertical magnet, but after the last vertical iinpulse has been delivered relay 104 deenergizes and breaks the circuit of relay 102. At the same time a circuit for slow acting relay 103 is closed as follows: ground at G, armature 116 and its working contact, oft normal spring 163 and its working contact, armature 121, and its resting contact, and the winding of relay 103 to battery. Relay 103'is energized before the slow acting relay 102 has had time to'deenergize and at its armature 120 closes a branch path over which ground Gr may be maintained in connection with conductor 05. :lelay 103 also connects up the rotary magnet 110 at armature 122 and disconnects the vertical magnet 109. Some other circuit changes produced by the shifting of the 011 normal springs may now be noticed. The circuit of the release magnet 112 is prepared at oil? normal spring 164, at off normal spring 162 the cut off relay 100 is disconnected, and by the shifting of oil normal spring 161 from its resting to its working-contact the circuit of the switch supervisory lamp U, which extends over conductor 98, is broken and a circuit is completed which extends over conductor 96 to the regular supervisory lamp L Lamp U is thus extinguished and lamp L is lighted. Thiscondition of the lamps indicates to the attendant that although the connector has been operated the called party has not answered.

The connector H is now ready to respond to the calling of the final digit, which is the digit'7. When the dial is operated in accordance with this digit a series of seven interruptions is produced in the line relay circuit causing this relay to deenergize as before described. Now, however, since relay 103 is energized, current impulses are transmitted to the rotary magnet 110. The circuit is the same as was described in the case of the vertical magnet except that it is switched over to the rotary magnet at armstnre 122 of relay 108. By the operation of the rotary magnet 110 the shaft of the switch is rotated step by step until the wipers are finally brought to rest in engagement with the bank contact in which is terminated the line of station A, these bank contacts being indicated in the drawing by reference characters MEL-145, inclusive. The slow acting relay 104 is energized as before, remaining in operated'position during the rotation of the switch, and at the back contact of its armature 124 breaks the normal energizing circuit of relay 103, immediately closing, however, another circuit for the same relay at the right hand working con tact of the same armature. Relay 103, therefore remains in operated position. It will be seen also that the circuit of slow act ing relay 102 is closed at the left hand working contact of armature 124 and this relay is also energized and maintained in operated position while the switch is rotating. The circuit changes brought about at armatures 117 and 119 are in this instance of no special consequence, the object of energizing relay 102' again being the preparation of a busy release circuit at armature 118. This is brought into use as follows: When the slow acting relay 104 falls back at the end of the rotation of the Switch, the circuits of relays 102 and 108 are both broken by arma ture 124, the circuit of the latter relay being immediately reestablished at the back contact of this armature. Assuming, now that the line of station A is busy when called, there will be a ground potential upon the test contact 144, and when relay 104 deenergizes, a circuit is closed through the release magnet 112 as follows: ground on test contact 144, test wiper 141, armature 123 and its resting contact, armature 118 and its working contact (slow acting relay 1 2 remaining in operated position for an instant), lower winding of busy test relay 105, off normal springs 164, and the winding of the release magnet 112 to battery. By the operation of release magnet 112 the switch is restored to normal position. When the switch shaft becomes completely restored the 051' normal springs are shifted back to their original condition and the release magnet circuit is broken. The busy test relay 105 is energized in series with the release magnet and establishes a locking circuit for itself which for all practical purposes may be considered as extending from the grounded conductor 95 by way of the upper high resistance winding of said relay to battery. The locking arrangement shown, however, may be used to save a contact spring, the upper winding of the relay 105 being switched on to the magnet circuit which on tends through relay 104 and either magnet 110 or 109 (the latter as soon as the switch becomes completely restored) to battery. Thus the magnet circuit is broken and a locking circuit is established also, with a minimum of contact springs. In its energized. position relay 105 connects a lead from the busy signaling machine Q to the lower heavy talking conductor, thereby giving the operator at the distant main exchange an audible busy signal.

Having explained the operations which take place when a busy line is called, we will now proceed with the establishment of the connection under consideration, it being assumed that the line of station A was idle when called. The switch wipers having been brought to rest in engagement with bank contacts 143-145, inclusive, as previously described, when the slow acting relay 104 deenergizes at the end of the rotation of the switch the circuit of the release magnet will not be cl(. sed.'because the test wiper 141 will find no ground potential on test contact 144. Nothing happens therefore until relay 102 deenergizes which occurs an instant later. A circuit is then completed which includes the switching relay 10S and the switching relay 146 of line switch C in series, extending as follows: grounded conductor 95, winding of relay 108, normally closed contact springs controlled by armature 132, resting contact of matures due to the fact that the line relay of the line switch has not been energized, and the line conductors are not connected through to the wipers of the line switch.

At the connector H relay 108 is energized in series with relay 1-16 and at its armature 132 breaks the rotary magnet circuit at the same time connecting the lead from the rotary magnet to its upper terminal in place of the conductor extending to the test wiper 1 11 This arrangement is another expedient used to economize in contact springs, and accomplishes the object intended which is to open the operating circuit of the rotary magnet and establish a locking circuit for relay 108. At its armature 133 relay 108 connects direct ground to the test wiper 141, thus rendering test contact 1414 and its multiples busy to other calls and at its armature 1341 relay 108 connects up the lower line wiper 141-2. It will be observed that the lower winding of the ring cut off relay 107 is connected to battery by the spring combination controlled by armature 132, and it follows therefore that the usual ringing circuit has now been established. Ringing current from generator Gen is projected out over the called line in the customary manner to operate the bridged ringer at station A, the return path for the ringing current including the upper heav y line conductor, the lower winding of the ring eut-oti' relay, the rotary magnet 110, and the grounded branch exchange battery.

lVhen the called subscriber responds by removing his receiver the ring cut-oft relay 10. is operated in the usual manner and establishes a locking circuit for itself at its armature 130, opens the ringing circuit at armatures 129 and 131, and at the working contacts of these same armatures finally completes the talking circuit through to the called line. Talking current is supplied to the transmitter at the called station through the windings of the double wound back bridge relay 106 which energizes immediately after the ring cut-ott' relay pulls up Supervision is also given to the operator at the main exchange and this operation will now be explained. hen the calling of the final digit was completed the operator of course restored the calling device key K and the relay 13 is thereby again inserted in the line relay circuit and is energized thereover. The supervisory lamp L which was temporarily extinguished during the dialing operation, is again lighted. Now when the relay 106 of the connector pulls up on the response of the called subscriber the line relay circuit extending from ground G and through the winding of relay 13 is broken at armature 128 of relay 106 and the line relay 101 is energized by a local circuit in the connector. Relay 13 is accordingly deenergized and extinguishes the lamp L this result being accomplished by the short-circuiting of the condenser C which permits the supervisory relay 5 to energize. It will be seen then that the main exchange operator is given the standard supervision.

hen the conversation is finished both subscribers will hang up their receivers. The replacement of the receiver at station A causes the lighting of the supervisory lamp L in the usual manner, while the replacement of the receiver at station A causes the lighting of supervisory lamp L through the falling back of relay 106 and the consequent energization of relay 13. Upon observing the lighted supervisory lamps the operator will know that the conversation is over with and she will accordingly pull down the connection. The release of the connector H is brought about following the deenergization of the line relay 101 which falls back when the lower line conductor is opened at armature 16 of relay 12. Relay 101 breaks the circuit of slow acting relay '103 which, upon deenergizing, closes the release magnet circuit at the resting contact of armature 120 and the switch is restored to normal. lVhen this occurs the busy lamp L at the attendants position and the supervisory lamp L which was lighted when the called party hung up, are both extinguished, whereupon all the equipment in use will have been restored and made ready for use in another call.

There is a certain class of main to branch exchange calls in which the main exchange subscribers simply desire connection with the company served by the branch exchange, not being familiar with its organization and being uncertain as to the department or individual who should handle the business in hand. These general calls are referred to the attendant operator at the branch exchange and are by her routed to their proper destinations. The process of establishing a connection of this class Will now beexplained. For this purpose it will be assumed that the subscriber at station A desires to obtain connection with Blank and Co, we will say, this being thecompany having the branch exchange equipment shown. The connection may be handled by the main exchange operator substantially as before described, the cord circuit O being used to connect the calling line with an idle trunk to the branch exchange which we will assume to be the trunk terminating in jack J Vhen the plug is inserted in jack J the line relay circuit extending to connector H is completed, relays 101 and 102 of the connector are energized, and the busy and switch supervisory lamps L and L at the at-te-ndants position are lighted, all as before explained. Since the call isto be turned over to'the attendant at the branch, the main exchange operator does not now operate her calling device, she doesnt know what number to call anyway,but instead she will throw her key K to ringing position momentarily. This operates the ring down relay 32 which is'bridged across the trunk at the attendants position, and this relay locks itself at its armature 35, the circuit being readily traceable over conductor 98 to the grounded off-normal spring 161 at the connector. Relay 32 also breaks the circuit of lamp L at armature 37 and closes the circuit of lamp L at armature 36.

Lamp L is the call signal and indicates to the attendant operator that she is being called from the main exchange.

The attendant operator answers by throwing her listening and calling device key K producing numerous circuit changes which will beexplained. To begin with, by the separation of contact springs 42 the locking circuit of relay 32 is broken, this relay being deenergized and the call signal lamp L being extinguished. By the closure of contact springs 43 the grounded conductor 97 is connected to relay 33 which energizes and establishes a locking circuit for itself at its armature 38. In addition, at its armature 39, relay 33 breaks the continuity of the lower heavy talking conductor and divides this conductor into two sections which are, however, inductively connected by the condenser C. At the same time the impedance coil 34 is connected to the section extending in the direction of the connector H, the effect being to substitute coil 34 for relay 13 in the line relay circuit. Relay 13 therefore deenergizes and short circuits condenser C by which operation the supervisory lamp L is extinguished and the -main exchange operator is advised that the attendant has answered. As a further result of the operation of key K the attendants calling device is inserted in the line relay circuit extending to the connector H, and this circuit will now be traced: ground at G winding of coil 34, working contact of armature 39 and the said armature, contact spring 40 and its working contact, con- (luctoi' :47, impulse springs of calling device S, contactsprings of releasing key K, conductor 48, and working contact of con.- tact spring 41 and the said spring to conductor 99, whence the circuit continues as previously traced to the connector H and through the line relay 101 to battery. A circuit in multiple with the above for the line relay 101 may be traced from ground G, through the winding of coil 34, working contact of spring 46 of key K and the said spring, to conductor 47 and thence over the previously traced circuit to the line relay 101. This circuit has no function at the present time. However, should the attendant operator be called upon to set up a connection to the main exchange for a branch exchange subscriber, the line relay 101 would not be energized by the operation of key K were it not for this multiple circuit. This multiple circuit enables the attendant operator to energize the line relay 101 and control the connector H. Returning now to the further effects brought about by the operation of the key K by the closure of contact springs 45 the attendant operators'head set is bridged across the trunk line as follows: upper trunk conductor 94, contact springs 45, right hand secondary winding of the induction coil, left hand secondary winding of the induction coil (and the receiver and condenser in parallel therewith), and conductor 50 to junction point 51, where it joins the previously traced circuit of the lower trunk line conductor (traced out as the line relay circuit).

The attendant; operator may now talk to the calling subscriber and ascertain his wants. F or convenience we will assume that it develops his wants can be best attended to by the department in which sta-, tion A is located. The operator will then ask the subscriber to wait a moment and will proceed to operate her calling device S first in accordance with the digit 6 and then the digit 7 for the purpose of controlling the connector H to complete the connection. During the operation of the calling device the shunt springs 52 therein are closed whenever the dial is away from its normal position to short circuit the impedance coil 34. The operation of the connector is the same as before described and need not be gone over again. Having finished calling the number the attendant operator may restore her key K thus removing her head set from in bridge of the trunk and cutting her calling device out'of the line relay circuit, the latter circuit remaining closed through the impedance coil 34, however, for relay 33 is still locked up. This enables the attendant to leave the line without giving the main exchange operator a false disconnect the trunk lineassociated therewith.

signal. lVhen the called subscriber answers relay .106 at the connector removes ground from the conductor 97 and breaks the looking circuit-oi relay 33 which thereupon deenergizes andrestores the line relay circuit over the lower heavy trunk conductor to its original condition. This places the supervisory lamp L under the control of the called party, and we have the same conditions existing as when the connection was i do so in theito-llowing manner: Assuming hat the trunk line shown inthe drawings is not in use, as indicated by the unlighted condition of busy lamp L, the attendant operator will actuatekey K momentarily. By this operation a circuit. is closed for relay 13 at the main exchange as follows: ground at G, winding of relay 13, upper right hand winding of the repeating coil R,

conductor 80, contacts of key K and the resistance 53 to battery- Upon energizing, relay 13 locks itself at its armature 20, and at its armature 19 closes the circuit of the line lamp L The line lamp is therefore lighted and i notities the main exchange operator that a call has been received over hen the operatorv plugs into the jack J to answer the call the cut-off relay 12 is energized and operates to break the locking circuit of relay 13 and extinguishes the line lamp L The connection can then be extended to any main exchange subscriber in the usual manner.

. Since the attendant operator can call in both directions over the trunk lines passing through her position, she can set up connections for the branch exchange subscribcrs if they should desire her to do so. Important. o'flicials of the company may at tinies'be too busy to bother with obtaining their own through main exchange connections, which necessarily involve some little waste of time, and will prefer to have these connections obtained for them by the attendant. Suppose the party at station A desires a main exchange connection and has no time to bother with it himself. He will remove his receiver, whereupon his line will be extended in the well known manner to an idle local connector through the medium of the individual line switch C. The sub ,scriber can now operate his calling device and by raising the connector tothe proper connection with a local trunk line leading to the attendant operators position. hen the attendant answers she is given the necessary data. on the desired connection and the branch exchange subscriber then hangs up his receiver. The attendant will now proceed to call the desired party in the main exchange as before explained and after obtaining the connection she will call back on the trunk line in the reverse direction to connect with the branch exchange subscriber who initiated the call.

The branch exchange subscribers may, however, call the main exchange direct it they so desire. The operation is initiated by removing the receiver, whereupon (if station A is calling) the line switch Coperates to extend the line of station A to a local connector, as before stated. By suit: able operation of the calling device the connector is now raised to the level in which the main branch exchange trunk lines are terminated, and a further operation of the connector results in the automatic selection of an idle one of these trunks. Assuming that the trunk line shown is the trunk selected, the connector wipers will have established connection with the bank contacts 150, 151, and 152 either directly or through a multiple thereof, depending on the switch in which these contacts are located; and the private wiper of the connector will place a ground on the test contact 151. By this means a circuit is closed for relay 100 of the connector H which, upon-energizing, disconnects the incoming trunk conductors from the connector at its armatures 113 and 115, and at its armature 114 disconnects the now grounded conductor 95 from the 011'- normal spring 161 of the connector. prevents the lighting of the switch supervisory lamp L at the attendants position, although the busy lamp L is lighted as usual. The connection to the trunk having been completed, the main exchange operator is signalled the same way as was described in the case where she was being called by the attendant, except that battery is connected to the upper trunk conductor by the local connector instead of by the operator. This will be readily understood when it is recalled that the upper wiper of an automatic connector is connected to battery after the connector has been operated, in certain types of connectors through a winding of the back bridge relay and in other types through a winding of the ring out off relay. In either case battery will be connected to This.

the. upper trunk line conductor and the relay 13 at the main exchange will be energized to signal the main exchange operator, after which the connection may be completed in the ordinary manner.

Having described my invention what 1 consider to be new and desire to have pro-- tected by Letters Patent will be pointed out in the appended claims.

What I claim is:

1. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, continuous two way trunk lines passing through said operators position and connecting said exchanges, and means including said trunk lines for completing inte-rexchange calls originating in either exchange.

2. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a continuous trunk .line passing through said oper-ators position and connecting said exchanges, and means whereby operators in the main exchange and calling subscribers in the branch exchange can complete interexchange connections over said trunk line.

3. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a continuous trunk line passing through said operators position and connecting said exchanges, means including said trunk line and an automatic switch at the branch exchange whereby a main exchangeoperator can complete an interexchange connection, and means including an other automatic switch at the branch exchange whereby a. branch exchange sub ing branch exchange subscriber can signal the attendant operator, and means including said trunk line whereby said attendant operator can complete interexchange connections originating incither exchange.

5. In a telephone system, a manual main exchange, and an automatic branch exchange, an attendant operators position at the branch exchange, a continuous trunk line connecting said exchanges and extending through said attendants position, means for establishing main to branch and branch to main exchange connections over said trunk line independent of the attendant operator, means for signalling the attendant from one end of said trunk line when her assistance is desired, and means whereby the attendant can answer when signalled and extend a connection over said trunk line in one direction when requested.

r-s I an attendant operators position at the] branch exchange, a continuous trunk line connecting said exchanges and extending through said attendants position, means for establishing main to branch and branch to main exchange connections over said trunk line independent of the attendant operator, a signal at the attendants position for indicating the idle or busy condition of said trunk line, and means whereby the attendant can connect with said trunk line and call in either direction thereover when the trunk line is not in use.

7. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, continuous two way trunk lines passing through said operators position and connecting said exchanges, means including said trunk lines for completing interexchange calls originating in either exchange, and signals at the attendants position for enabling the attendant to supervise all calls originating in the main exchange.

8. In a teiephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, continuous two way trunk lines passing through said operators position and connecting said exchanges, means including said trunk lines for completing interexchange calls originating in either exchange, and busy signals for said trunk lines "for advising the attendant operator when the trunk lines are in use.

9. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, continuous .two way trunk lines passing through said operators position and connecting said exchanges, means including said trunk lines for completing interexchange calls originating in either exchange, a busy signal and a supervisory signal foreach trunk line at the at tendants position, means for actuating the busy signals whenever the trunk lines are in use, and means for suitably controlling the supervisory signals to give the attendantv answering and disconnect supervision over calls originating in the main exchange.

10. In a telephone system, a manual main exchange and an automatic branch exchange, and an attendant operators position at the branch exchange, a continuous inter-exchange trunk line passing through the attendants position and terminating in an automatic switch in the branch exchange, means for establishing mainto branch exchange connections through the medium of said trunk line and switch, and a signal at the attendants position controlled by said switch when the trunk line is in use for advising the operator as to whether or not the said switch has been operated.

11. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a continuous inter-exchange trunk line passing through the attendants position and terminating in an automatic switch in the branch exchange, means for establishing main to branch ex change connections through the medium of said trunk line and switch, a signal for giving the attendant answering and disconnect supervision over such connections, and a second signal for giving the attendant direct supervision over said switch to advise her of its normal or oif normal condition.

12. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a trunk line coming from the main exchange and extending through the attendants position to an automatic switch, means including said trunk line and switch whereby an operator in the main exchange can extend a connection to a subscribers line in the branch exchange,

means whereby the main exchange operator can signal the attendant operator if she so desires,and a supervisory signal controlled in one case by the response of the called subscriber and in the other case by the response of the attendant.

18. In a telephone system, a main ex change and a branch exchange, a trunk line connecting said exchanges, operators at both exchanges cooperating to complete main to branch exchange .connections, means for giving the main exchange operator answering supervision when the branch operator comes in on the trunk to assist in setting up a connection, means whereby the branch operator after she has completed the connection can leave thetrunk Without giving the main exchange operator a disconnect signal, means for giving the branch operator answering supervision upon the] response of the called subscriber, and means for giving both operators disconnect supervision when the called subscriber hangs up his receiver.

14. In a telephone system, a manual main exchange and an automatic branch exchange, a trunk line connecting said exchanges and terminating in an automatic switch in the branch exchange, operators at both exchanges cooperating to' establish main to branch exchange connections, means for signalling the branch operator over said trunk line when. a connection is wanted, means for giving the main exchange operator answering supervision when the branch operator comes in on the trunk, means whereby thebranch operator can operate said switch to complete the desired connection, means whereby the branch operator can leave the trunk before the calledparty answers without giving the main exchange operator a disconnect signal, means for giving the branch operator answering supervision when the called party answers, and means for giving both operators disconnect supervision when the called party hangs up his receiver.

15. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a trunk line coming from the main exchange and extending through the attendants position to an auto matic switch, means whereby a main exchange operator can signal the attendant operator when a branch exchange connec tion is wanted, a supervisory signal con trolled by the response of the attendant to notify the main exchange operator there- 01", means whereby the attendant operator can control said switch to complete the desired connection, and means whereby the attendant can disconnect herself from the trunk line before the called subscriber answers without affecting said supervisory signal.

16. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a trunk line coming from the main exchange and extending through the attendants position to an automatic switch, means whereby a main exchange operator can signal the attendant operator when a branch exchange connection is wanted, a supervisory signal controlled by the response of the attendant to notify the main exchange operator thereof, means whereby the attendant operator can control said switch to complete the desired connection, means whereby the attendant can disconnect herself from the trunk line before the called subscriber answers without affect signalfor the attendant operator, and meansfor controlling said second signal when the called subscriber answers.

17. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a trunk line coming from the main exchange and extending through the attendants position to an automatic switch, means whereby a main exchange operator can signal the attendant operator when a branch exchange connection is wanted, a supervisory signal controlled by the response of the attendant to notify the main exchange operator thereof, means whereby the attendant operator can control said switch to complete the desired connection, means whereby the attendant can disconnect herself from the trunk line before the cal ed subscriber answers without alfect ing said supervisory signal, a supervisory signal for the-attendant operator, means for controlling said second signal when the called subscriber answers, and means for controlling both signals at the same time when the called subscriber hangs up his receiver.

18. In a telephone system, a two way trunk line extending from first exchange to a second exchange, call and supervisory signals at the first exchange, a relay for controlling both signals, means for controlling said relay over one conductor of said trrnl; line independent of the other to control said call signal on incoming calls, and means for controlling said relay over the other conductor of said trunk line independent of the first to control said supervisory signal'on outgoing calls. 7

19. In a telephone system, a two way trunk line connecting two exchanges, a repeating coil in said trunk at one of said ex changes, a relay connected from the middle point of the outgoing side of said repeat ing coil to ground, means for establishing a circuit for said relay including only one talking conductor of said trunk line and ground return when calls are extendedin one direction, and means for establishing another circuit for said relay including the other conductor of said trunk line and ground return when calls are extended in the other direction.

20. In a telephone system,,a two way trunk line connecting t-woexchanges, a repeating coil in said trunk at one of said.

exchanges, a relay connected from the middle point of the outgoing side of said repeating coil to ground, means for establishing a circuit for said relayv including only one talking conductor of said trunk line and ground return when calls are extended in one direction, means for establishing another circuit for said relay including the other conductor of said trunk line and ground return when calls are extended in the other direction, call and supervisory signals. means for controlling said relay over one of its circuits to control said call signal, and means for controlling said relay over the other of its circuits to control said supervisory signal.

21. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position at the branch exchange, a trunk line coming from the main exchange and extending through the attendents position to an automatic switch at'the branch exchange, means whereby an operator at the main exchange can signal the attendant operator over said trunk, a listening key at the attendants position for answering the call, and a calling device connected in said trunk in readiness to operate said switch-whenever said key is actuated. a

22. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators position atthe branch exchange, a trunk line comingtrom the main exchange and extending through the attendants position ,to an automatic switch at the branch exchange, meansfor signalling the attendant operator over said. trunk when a main to branch exchange connection is desired, a listening keycat the attendants position for, answering they call, a calling devicetor operating said switch, and means whereby the actuation of said hey serves to connect the said calling device in the trunk so that the attendant can control said switch to complete the connection. 23. In a telephone system, a trunk line connecting a manual exchange with an automatic exchange, a call signal, at the manual end of said trunk, an automatic switch at the automatic end of said trunk, and, separate controlling circuits for said signal and switch, each controlling circuit including one conductor of said trunkline independent of the other.

24. In a telephone system, a two. way trunk line connecting a manual exchange with an automatic exchange, a call signal at the manual end and an automatic switch at the automatic end of said trunk, means for controlling said signal over a singletalking conductor of said trunk in obtaining an automatic to manual connection, and means for controlling said switch over the other talking conductorv of said trunk independent of the first in obtaining a manual to automatic connection. 1

25. In a telephone system, a manual exchange and an automatic exchange, a trunk line connecting the two and terminating; in an automatic switch in the automatic exchange, means for connect-ing with said trunk at the manual exchange and for establishing a control circuit for said switch over one of the talking conductors of said trunk independant of the other, a call signal for said trunk at the manual exchange, and means including another automatic switch in the branch exchange for connecting with said trunk and for establishing a control circuit for said signal over the other talk ing conductor of said trunk independent of the first. 26. In a telephone system, main and branch exchanges, a trunk line connecting said exchanges and terminating in an automatic switch at the branch exchange, means for setting up a main to branch exchange connection through the medium of said trunk line and switch, said means including means for establishing a control circuit for said switch over one'conductor of said trunk line while maintaining the other conductor main free of battery connections at the branch exchange, and means for breaking said control circuit when the called subscriber answers and for locally controlling said connector thereafter, whereby both conductors ofsaidtrunk line are kept free from battery connections at the branch exchange during conversation.

27. In a telephone system, a manual main exchange and an automatic branch exchange, an attendant operators switchboard at the branch exchange, a continuous twoway trunk line passing through said switchboard and connecting .said exchanges, a jack in which said trunkline terminates at the exchange, progressively movable switches associated with said trunk line at the branch exchange, means including said trunk line, jack, and one of said switches for completing main to branch exchange calls,and means including said trunk line, jack, and another one of said switches for completing branch to main exchange calls. 28. In a telephone system, a manual main exchange and an automatic branch ex change, an attendant operators position at the branch exchange, -a continuous trunk line connecting said exchanges and extending through said attendants position, means for establishing main to branch and branch to main exchange connections over said trunk line independent of the attendant operator, means for signalling the attendant over said trunk line when her assistance is desired by a subscriber in either exchange, and means whereby the attendant can answer when signalled and extend the required connection over said trunk line.

29. In a telephone system, two exchanges, means including an interoflice trunk line and an automatic switch in the second exthe operator incidental to handling the call,

a locking circuit for said second relay, a relay in saidswitch controlled by the subscriber on the called line, and means controlled by said last mentioned relay for opening said locking circuit and for controlling the circuit of said supervisory relay after said second relay has deenergized.

80. In a telephone system, an interoilice trunk line connecting two exchanges, means whereby an operator in the first exchange can signal an; operator in the second exchange over said trunk line, a supervisory signal at the first exchange, a relay at the. second exchange initially energized by the operator at the second exchange when she answers the call, means whereby said relay controls said signal to give answering supervision to the first operator, automatic switching mechanism controlled by the second operator for extending said trunk to a called line, a locking circuit for maintaining said relay energized after the sec ond operator leaves the trunk upon con1- pleting the connection, and means controlled by the called subscriber on removing his receiver for opening said locking circuit and for maintaining the answered indication by said signal until the receiver is replaced.

Signed by me at Chicago, Cook County, Illinois, this 14th day of April, 1920. s

' CLARENCE E. LOMAX. 

